1. Field of Invention
This invention relates to colorants for plastics and, in particular, to a stable liquid color composition.
2. Brief Statement of the Prior Art
Colors have commonly been incorporated in the pellets of molding resins supplied to fabricators. The desire for flexibility in changing color of molded parts and to avoid large inventories of colored pellets has promoted the addition of colors during the molding or fabrication of plastic products. Finely powdered dyes and pigments have been employed, however, many of these form hazardous dusts, presenting inhalation toxicity problems and present contamination and clean-up problems. The pigments have also been dispersed in various liquids to provide liquid colorants that can be metered into the molding equipment with a small injection pump. Since most of the colorants are solid pigments, and are often high density metal oxides and salts, difficulties have been experienced in providing a stable suspension of these materials in a liquid vehicle. Additionally, the choice of a suitable liquid for use as the vehicle for the pigment suspension is limited since the liquid must be compatible with the resin, must be inert under the molding conditions, and must resist weathering and solvent attack in the finished product. Heretofore, no liquid colorant composition has been provided which has these necessary properties. The most promising prior attempts have resulted in liquid suspensions of limited stability which must be stirred prior to use to redisperse the settled pigments. The necessary stirring is undesirable, not only because of the additional step, but also because stirring often incorporates air bubbles in the liquid, causing errors in the metering system and imperfections in the color of the molded products.